How to Size a Home Furnace

Finding the appropriate size furnace is important. On one hand, a furnace that is too small won't be able to heat the area effectively. On the other hand, a furnace that is too large will short-cycle, causing it to turn off and on more often, which will use unnecessary energy and cost you money.

Things You'll Need

• Paper
• Pen
• Calculator

Instructions

Furnace Sizing

1. Determine the amount of output Btu you need to heat the area; output Btu is a measure of the amount of heat the furnace produces. As a general rule, start with about 30-35 output Btu per square foot; however, this can vary depending on climate and how well-insulated your house is.

2. Look around for furnaces that match your requirements in terms of size, price, etc.

3. Determine the output Btu of the furnaces you are considering. If the specifications for the furnace don't list output Btu, see if they list input Btu, a measure of the energy required to run the furnace. To find output BTU, multiply the furnace's input BTU by its efficiency.

Tips & Warnings

• Hiring a contractor will provide the most accurate furnace sizing information. Professional contractors have the tools necessary to take factors like insulation level into account when determining size.

• Many furnace specification lists will advertise input BTU; be sure to check the fine print and look for output BTU or calculate it yourself.

References

• Alpine Home Repair
• Home Tips

Resources

• AC Direct